The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus in which image formation is performed such that a toner image formed on a surface of a carrier is transferred to an intermediate transfer belt for transferring the toner image to recording medium.
Also, the present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus that performs image formation while rotary revolving a plurality of developing cartridges.
Conventionally, there is known an image forming apparatus of electrophotographic recording mode that exposes and forms an electrostatic latent image on a surface of a carrier made of a photoreceptor. In this image forming apparatus, a toner image, which is obtained by toner developing the electrostatic latent image and carried on the carrier surface, is transferred to recording medium such as recording paper, thus providing image formation. This electrostatic latent image is toner developed such that a developing roller opposed to the carrier surface is rotated to transfer and affix, to the carrier surface, toner on the surface of the developing roller. This developing roller is supplied with toner as a supply roller rotating in a toner storing space rotates in press contact therewith.
As this image forming apparatuses adopting the electrophotographic recording mode, there is an apparatus configured capable of housing in a rotary unit a plurality of developing cartridges that each include a container for storing toner therein together with the developing roller opposed to the carrier and the supply roller. In this image forming apparatus, the developing cartridge can be switched to be set at a developing position opposed to the carrier by rotating the rotary unit about a rotational shaft.
Consequently, such an image forming apparatus is configured capable of housing in the rotary unit (attaching to the rotary unit) developing cartridges storing toners of yellow (Y), magenta (M), cyan (C), and black (K) as the developing cartridges for affixing toner to the carrier surface. Thereby, a color image obtained by overlapping the individual colors can be formed by sequentially switching the developing cartridges. With this configuration, it is possible to form a monochrome image formed with toners of a single color, e.g., a black-and-white monochrome image formed with the toner of black (K) (hereinafter also referred to simply as a monochrome image).
Besides, it is proposed that the image forming apparatus provided with the rotary unit capable of attaching thereto a plurality of developing cartridges which stores toners of the same color (mainly black). With this configuration, the rotary unit is rotated at each timing, such as of when toner runs out, to sequentially switch the developing cartridges to be put to use. This reduces the frequency of toner replenishing operations, thus making it possible to realize continuous formation of the monochrome image over a long period (e.g., see JP-A-2002-351190 and JP-A-2003-316106).
However, such an image forming apparatus of electrophotographic recording mode need maintain image quality by refreshing, such as agitating, the stored toner in the container. In contrast, to form a color image, the image forming apparatus including the rotary unit sequentially switches the developing cartridges to be opposed to the carrier. Therefore, the developing cartridges are inverted upside down with the rotation of the rotary unit for performing this developing cartridge switching operation. Thereby, toners in the container are once mixed together to appropriately refresh the stored toner, thus making it possible to maintain image quality (e.g., see JP-A-2002-351190).
However, to form a monochrome image, the same developing cartridge is continuously used. Therefore, to perform an image forming operation (developing operation) in succession, there is a need to provide an agitating (adjusting) member and refreshing the stored toner during the operation.
Besides, as the image forming apparatus provided with the rotary unit, there is an apparatus contrived as follows. That is, a partition plate for partitioning off a small space in which the supply roller rotates is provided in the developing cartridge (container). And, the stored toner is appropriately replenished (adjusted) into the space in which the supply roller operates, thereby preventing toner to be supplied to the developing roller from accumulating around the supply roller over a long period, thus maintaining image quality with higher reliability. Even with this configuration, to form a color image, the developing cartridge is inverted upside down with the rotation of the rotary unit during the developing cartridge switching operation, thereby enabling appropriate replenishment of the stored toner to the space in which the supply roller operates (e.g., see JP-A-2002-351190).
However, similarly, to form a monochrome image, the same developing cartridge is continuously used. Therefore, to perform the image forming operation (developing operation) in succession, there is a need to provide a replenishing member which replenishes the stored toner to the supply roller side during the operation.
Further, the following can be considered as the adjusting member of agitating and replenishing the stored toner in the developing cartridge for forming a monochrome image. That is, at the timing of when there arises a need to adjust the stored toner, for example, when a pre-set amount of image formation is provided, as with color image formation, the stored toner is appropriately adjusted by rotating the rotary unit to invert the developing cartridge upside down.
However, when the same developing cartridge is continuously used to form a monochrome image, the stored toner in the developing cartridge is adjusted by rotating the rotary unit, which thus interrupts image formation during this stored toner adjusting operation. A predetermined amount of image formation is pre-set as a criterion for determining whether a stored toner adjusting timing is reached or not, in which state this stored toner adjusting operation need be repeatedly performed each time this amount of image formation is reached.
Since this criterion of determination as to whether or not to perform the stored toner adjusting operation is normally set to make allowance, this adjusting operation is sometimes carried out although allowance still remains before the actual timing of requiring adjustment of the stored toner. For example, even when an image data recording, and forming process is ready to be completed with image formation on one more recording medium, the image formation is interrupted and the stored toner adjusting operation is forcibly carried out. Consequently, there is the problem of reducing an image forming speed at which to complete recording and forming of image data, i.e. a so-called throughput.
Further, as the adjusting member of agitating and replenishing the stored toner in the developing cartridge for forming a monochrome image, as with color image formation, it can be considered that the stored toner is appropriately adjusted by rotating the rotary unit to invert the developing cartridge upside down.
However, to form a monochrome image, when the stored toner in the developing cartridge is adjusted by rotating the rotary unit, under a normal image forming control, image formation is interrupted during this stored toner adjusting operation. This reduces an image forming speed at which to complete the recording and forming of image data, i.e., a so-called throughput.
Furthermore, as such an image forming apparatus of electrophotographic recording mode, there is an apparatus configured as follows. That is, the toner image obtained by developing the electrostatic latent image on the carrier surface is once delivered to an intermediate transfer belt before being transferred to the recording medium. Thus, a toner image such as a color image is formed on this intermediate transfer belt and thereafter is transferred to the recording medium to provide image formation (e.g., see JP-A-2002-351190).
In this image forming apparatus provided with the intermediate transfer belt, the intermediate transfer belt rotates endlessly in accordance with the transport of the recording medium and the rotation of the carrier (toner image), whereby the toner image on the carrier surface is received by the intermediate transfer belt and then is transferred therefrom to the recording medium, thus providing image formation. However, to form a color image, there is a need to switch the developing cartridge in the course of the rotation of the intermediate transfer belt. Consequently, this intermediate transfer belt is formed longer than the transport-direction (sub-scan direction) length of the recording medium (toner image) designed capable of forming the color image thereon, by at least an amount capable of securing the switching operation period of the aforesaid developing cartridge.
However, to form a monochrome image, there is no need to switch the developing cartridges. Therefore, a region of the intermediate transfer belt for securing the developing cartridge switching operation period is not necessary in carrying out a normal operation.
Here, for example, A4 size recording paper (recording medium) is in general use in Japan, while recording paper of slightly larger size than A4 size, i.e. of legal size is also often used in foreign countries. Consequently, it is convenient if even a color image forming apparatus for A4 size use can be used to form a monochrome image such as a text on the recording paper of legal size.